Internet Assigned Numbers Authority • Domains • Protocols • Numbers • About Interior Gateway Protocol (IGP) Parameters Created 2017-12-18 Last Updated 2025-09-16 Available Formats [IMG] XML [IMG] HTML [IMG] Plain text Registries Included Below • IGP Algorithm Types • IGP MSD-Types • Link Attribute Application Identifiers • IGP Metric-Type • IGP Flexible Algorithm Definition Flags • Path Computation Element (PCE) Capability Flags • PCE Discovery (PCED) Sub-TLV Type Indicators • IGP Algorithm Type For Computing Flooding Topology • IGP Flex-Algorithm Path Computation Rules IGP Algorithm Types Registration Procedure(s) Standards Action Reference [RFC8665] Available Formats [IMG] CSV Value Description Reference Shortest Path First (SPF) algorithm based on link metric. This is the standard shortest path algorithm as computed 0 by the IGP protocol. Consistent with the deployed practice for link-state protocols, Algorithm 0 permits any node [RFC8665] to overwrite the SPF path with a different path based on its local policy. Strict Shortest Path First (SPF) algorithm based on link metric. The algorithm is identical to Algorithm 0 but 1 Algorithm 1 requires that all nodes along the path will honor the SPF routing decision. Local policy at the node [RFC8665] claiming support for Algorithm 1 MUST NOT alter the SPF paths computed by Algorithm 1. 2-127 Unassigned 128-255 Flexible Algorithms [RFC9350, Section 4] IGP MSD-Types Registration Procedure(s) Expert Review Expert(s) Uma Chunduri, Jeff Tantsura Reference [RFC8491][RFC9702] Note When this registry is modified, the YANG module "iana-msd-type" must be updated as defined in [RFC9702]. Available Formats [IMG] CSV Value Name Data Plane Reference 0 Reserved [RFC8491] 1 Base MPLS Imposition MSD MPLS [RFC8491] 2 ERLD-MSD MPLS [RFC9088] 3 Readable Label Depth MPLS [RFC9789] 4-40 Unassigned 41 SRH Max SL SRv6 [RFC9352] 42 SRH Max End Pop SRv6 [RFC9352] 43 Unassigned 44 SRH Max H.encaps SRv6 [RFC9352] 45 SRH Max End D SRv6 [RFC9352] 46-250 Unassigned 251-254 Experimental Use [RFC8491] 255 Reserved [RFC8491] Link Attribute Application Identifiers Registration Procedure(s) Expert Review Expert(s) Les Ginsberg, Chris Hopps Reference [RFC9479] Available Formats [IMG] CSV Bit Name Reference 0 RSVP-TE (R-bit) [RFC9479] 1 Segment Routing Policy (S-bit) [RFC9479] 2 Loop-Free Alternate (F-bit) [RFC9479] 3 Flexible Algorithm (X-bit) [RFC9350, Section 12] 4-63 Unassigned IGP Metric-Type Reference [RFC9350][RFC9843] Available Formats [IMG] CSV Range Registration Procedures 0-127 Standards Action 128-255 User-Defined Metric Type Description Reference Allowed in Generic-Metric 0 IGP Metric [RFC9350, Section 5.1] No 1 Min Unidirectional Link Delay as defined in [RFC8570, Section 4.2] and [RFC7471, [RFC9350, Section 5.1] No Section 4.2] 2 Traffic Engineering Default Metric as defined in [RFC5305, Section 3.7] and Traffic [RFC9350, Section 5.1] No Engineering Metric as defined in [RFC3630, Section 2.5.5] 3 Bandwidth Metric [RFC9843] Yes 4-127 Unassigned 128-255 Reserved for User-Defined Metric [RFC9843] Yes IGP Flexible Algorithm Definition Flags Registration Procedure(s) Standards Action Reference [RFC9350] Available Formats [IMG] CSV Bit Name Reference 0 Prefix Metric Flag (M-flag) [RFC9350, Sections 6.4 and 7.4] Path Computation Element (PCE) Capability Flags Registration Procedure(s) IETF Review Reference [RFC9353] Available Formats [IMG] CSV Bit Capability Description Reference 0 Path computation with GMPLS link constraints [RFC5088] 1 Bidirectional path computation [RFC5088] 2 Diverse path computation [RFC5088] 3 Load-balanced path computation [RFC5088] 4 Synchronized paths computation [RFC5088] 5 Support for multiple objective functions [RFC5088] 6 Support for additive path constraints (max hop count, etc.) [RFC5088] 7 Support for request prioritization [RFC5088] 8 Support for multiple requests per message [RFC5088] 9 Global Concurrent Optimization (GCO) [RFC5557] 10 P2MP path computation [RFC8306] 11 Active stateful PCE capability [RFC8231] 12 Passive stateful PCE capability [RFC8231] 13 Active Stateful PCE with P2MP [RFC8623] 14 Passive Stateful PCE with P2MP [RFC8623] 15 Stateful PCE Initiation with P2MP [RFC8623] 16 FlowSpec [RFC9168] 17 TCP-AO Support [RFC9353] 18 PCEP over TLS support [RFC9353] 19-31 Unassigned PCE Discovery (PCED) Sub-TLV Type Indicators Registration Procedure(s) Standards Action Reference [RFC9353] Available Formats [IMG] CSV Value Description Reference 0 Reserved [RFC9353][RFC5088] 1 PCE-ADDRESS [RFC9353][RFC5088] 2 PATH-SCOPE [RFC9353][RFC5088] 3 PCE-DOMAIN [RFC9353][RFC5088] 4 NEIG-PCE-DOMAIN [RFC9353][RFC5088] 5 PCE-CAP-FLAGS [RFC9353][RFC5088] 6 KEY-ID [RFC9353] 7 KEY-CHAIN-NAME [RFC9353] 8-65535 Unassigned IGP Algorithm Type For Computing Flooding Topology Registration Procedure(s) Expert Review Expert(s) Unassigned Reference [RFC-ietf-lsr-dynamic-flooding-18] Available Formats [IMG] CSV Value Description Reference 0 Reserved for centralized mode [RFC-ietf-lsr-dynamic-flooding-18] 1-127 Unassigned 128-254 Reserved for Private Use [RFC-ietf-lsr-dynamic-flooding-18] 255 Reserved [RFC-ietf-lsr-dynamic-flooding-18] IGP Flex-Algorithm Path Computation Rules Registration Procedure(s) Expert Review Expert(s) Unassigned Reference [RFC-ietf-lsr-igp-flex-algo-reverse-affinity-12] Available Formats [IMG] CSV Sequence Number Description Reference Check if any exclude Administrative Group rule is part of the Flex-Algorithm Definition. If such exclude rule exists, check if 1 any color that is part of the exclude rule is also set on the link. [RFC9350, Section 13] If such a color is set, the link MUST be pruned from the computation. Check if any exclude SRLG rule is part of the Flex-Algorithm 2 Definition. If such exclude rule exists, check if the link is part [RFC9350, Section 13] of any SRLG that is also part of the SRLG exclude rule. If the link is part of such SRLG, the link MUST be pruned from the computation. Check if any include-any Administrative Group rule is part of the Flex-Algorithm Definition. If such include-any rule exists, check 3 if any color that is part of the include-any rule is also set on [RFC9350, Section 13] the link. If no such color is set, the link MUST be pruned from the computation. Check if any include-all Administrative Group rule is part of the Flex-Algorithm Definition. If such include-all rule exists, check 4 if all colors that are part of the include-all rule are also set on [RFC9350, Section 13] the link. If all such colors are not set on the link, the link MUST be pruned from the computation. If the Flex-Algorithm Definition uses something other than the IGP metric (Section 5 of [RFC9350]), and such metric is not advertised 5 for the particular link in a topology for which the computation is [RFC9350, Section 13] done, such link MUST be pruned from the computation. A metric of value 0 MUST NOT be assumed in such a case. Check if any exclude FAEMB rule is part of the Flex-Algorithm definition. If such exclude rule exists and the link has Maximum 6 Link Bandwidth advertised, check if the link bandwidth satisfies [RFC9843, Section 6] the FAEMB rule. If the link does not satisfy the FAEMB rule, the link MUST be pruned from the Flex-Algorithm computation. Check if any exclude FAEMD rule is part of the Flex-Algorithm definition. If such exclude rule exists and the link has Min 7 Unidirectional link delay advertised, check if the link delay [RFC9843, Section 6] satisfies the FAEMD rule. If the link does not satisfy the FAEMD rule, the link MUST be pruned from the Flex-Algorithm computation. Check if any exclude reverse Admin Group rule is part of the Flex-Algorithm definition. If such exclude rule exists, check if 8 any Admin Group that is part of the exclude rule is also set on the [RFC-ietf-lsr-igp-flex-algo-reverse-affinity-12, Section 11] link in the reverse direction. If such Admin Group is set on the link in the reverse direction, the link MUST be pruned from the computation. Check if any include-any reverse Admin Group rule is part of the Flex-Algorithm definition. If such include-any rule exists, check 9 if any Admin Group that is part of the include-any rule is also set [RFC-ietf-lsr-igp-flex-algo-reverse-affinity-12, Section 11] on the link in the reverse direction. If no such Admin Group is set on the link in the reverse direction, the link MUST be pruned from the computation. Check if any include-all reverse Admin Group rule is part of the Flex-Algorithm definition. If such include-all rule exists, check 10 if all Admin Groups that are part of the include-all rule are also [RFC-ietf-lsr-igp-flex-algo-reverse-affinity-12, Section 11] set on the link in the reverse direction. If all such Admin Groups are not set on the link in the reverse direction, the link MUST be pruned from the computation. Licensing Terms